package com.atguigu.tree;


public class SegmentTree<E> {
    private E[]tree;
    private E[]data;
    private Merger<E>merger;
    public SegmentTree(E[]arr,Merger<E>merger){
        this.merger=merger;
        data= (E[]) new Object[arr.length];
        for (int i = 0; i < arr.length; i++) {
            data[i]=arr[i];
        }
        tree= (E[]) new Object[arr.length*4];
        buildSegmentTree(0,0,data.length-1);
    }
    //在treeIndex的位置创建表示区间[1...r]的线段树
    //后序遍历的思想
    private void buildSegmentTree(int treeIndex, int l, int r) {
        if(l==r){
            tree[treeIndex]=data[l];
            return ;
        }
        int leftTreeIndex=leftChild(treeIndex);
        int rightTreeIndex=rightChild(treeIndex);
        int mid=l+(r-l)/2;
        buildSegmentTree(leftTreeIndex,l,mid);
        buildSegmentTree(rightTreeIndex,mid+1,r);
        tree[treeIndex]=merger.merge(tree[leftTreeIndex],tree[rightTreeIndex]);
    }

    public int getSize(){
        return data.length;
    }
    public E get(int index){
        if(index<0||index>=data.length){
            throw new IllegalArgumentException("Index is illegal");
        }
        return data[index];
    }
    private int leftChild(int index){
        return index*2+1;
    }
    private int rightChild(int index){
        return index*2+2;
    }
    //返回区间[queryL,queryR]的值
    public E query(int queryL,int queryR){
        if(queryL<0||queryL>=data.length||queryR<0||queryR>=data.length||queryL>queryR){
            throw new IllegalArgumentException("Index is illegal");
        }
        return query(0,0,data.length-1,queryL,queryR);
    }
    //在以treeIndex为根的线段树中[l...r]的范围里，搜索区间[queryL...queryR]的值
    private E query(int treeIndex,int l,int r,int queryL,int queryR){
        if(l==queryL&&r==queryR){
            return tree[treeIndex];
        }
        int mid=l+(r-l)/2;
        int leftTreeIndex=leftChild(treeIndex);
        int rightTreeIndex=rightChild(treeIndex);
        if(queryL>=mid+1){
            return query(rightTreeIndex,mid+1,r,queryL,queryR);
        }else if(queryR<=mid){
            return query(leftTreeIndex,l,mid,queryL,queryR);
        }
        E leftResult=query(leftTreeIndex,l,mid,queryL,mid);
        E rightRsult=query(rightTreeIndex,mid+1,r,mid+1,queryR);
        return merger.merge(leftResult,rightRsult);
    }
    //将index位置的值，更新为e
    public void set(int index,E e){
        if(index<0||index>=data.length){
            throw new IllegalArgumentException("Index is illegal");
        }
        data[index]=e;
        set(0,0,data.length-1,index,e);
    }
    //在以treeIndex为根的线段树中更新index的值为e
    private void set(int treeIndex,int l,int r,int index,E e){
        if(l==r){
            tree[treeIndex]=e;
            return ;
        }
        int mid=l+(r-l)/2;
        int leftTreeIndex=leftChild(treeIndex);
        int rightTreeIndex=rightChild(treeIndex);
        if(index>=mid+1){
            set(rightTreeIndex,mid+1,r,index,e);
        }else{
            set(leftTreeIndex,l,mid,index,e);
        }
        tree[treeIndex]=merger.merge(tree[leftTreeIndex],tree[rightTreeIndex]);
    }

    @Override
    public String toString() {
        StringBuilder res=new StringBuilder();
        res.append("[");
        for(int i=0;i<data.length;i++){
            if(i!=data.length-1){
                res.append(tree[i]).append(",");
            }else{
                res.append(tree[i]);
            }
        }
        res.append("]");
        return res.toString();
    }
}
